Clock recovery and data recovery for programmable logic devices

ABSTRACT

Various techniques are provided to efficiently implement user designs incorporating clock and/or data recovery circuitry and/or a deserializer in programmable logic devices (PLDs). In one example, a method includes receiving a serial data stream, measuring time periods between signal transitions in a serial data stream using at least one Grey code oscillator, and generating a recovered data signal corresponding to the serial data stream by, at least in part, comparing the measured time periods to one or more calibration time periods. In another example, a system includes a Grey code oscillator configured to increment a Grey code count between signal transitions in a serial data stream, and a Grey code converter configured to convert the Grey code count approximately at the signal transitions to a plurality of binary counts each corresponding to a time period between one or more signal transitions in the serial data stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to and the benefit of U.S.Provisional Patent Application 62/385,247 filed Sep. 8, 2016 andentitled “CDR IN PROGRAMMABLE LOGIC,” U.S. Provisional PatentApplication 62/385,359 filed Sep. 9, 2016 and entitled “CDR INPROGRAMMABLE LOGIC,” U.S. Provisional Patent Application 62/385,437filed Sep. 9, 2016 and entitled “CDR IN PROGRAMMABLE LOGIC,” and U.S.Provisional Patent Application 62/452,213 filed Jan. 30, 2017 andentitled “CDR IN PLB,” which are all hereby incorporated by reference intheir entirety.

TECHNICAL FIELD

The present invention relates generally to programmable logic devicesand, more particularly, to clock and/or data recovery in programmablelogic devices.

BACKGROUND

Programmable logic devices (PLDs) (e.g., field programmable gate arrays(FPGAs), complex programmable logic devices (CPLDs), field programmablesystems on a chip (FPSCs), or other types of programmable devices) maybe configured with various user designs to implement desiredfunctionality. Typically, the user designs are synthesized and mappedinto configurable resources (e.g., programmable logic gates, look-uptables (LUTs), embedded hardware, or other types of resources) andinterconnections available in particular PLDs. Physical placement androuting for the synthesized and mapped user designs may then bedetermined to generate configuration data for the particular PLDs.

PLDs are commonly used to deserialize serialized input data streams,and, as a result, are often implemented with a limited number ofdedicated deserializer blocks that can be used to recover or extractserialized data from input data streams. However, such blocks requiresignificant area in order to be implemented in a PLD, and there arecorrespondingly limited routing resources that can be used to implementuser designs incorporating such dedicated deserializer blocks. Moreover,such blocks often employ a phase locked loop or an accurate clock tooversample the data stream, which can present a significant timingburden on general routing and, in particular, clock-related circuitry,all of which can be in limited supply in a relatively inexpensive PLD.Such constraints can severely limit the scope of user designs that canbe implemented in PLDs, can result in degraded PLD performance, and cansignificantly increase the time and processing resources needed todetermine connection routings for the PLD.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a programmable logic device (PLD)in accordance with an embodiment of the disclosure.

FIG. 2 illustrates a block diagram of a logic block for a PLD inaccordance with an embodiment of the disclosure.

FIG. 3 illustrates a design process for a PLD in accordance with anembodiment of the disclosure.

FIG. 4 illustrates a schematic diagram of a clock and/or data recoverydeserializer for a PLD in accordance with an embodiment of thedisclosure.

FIG. 5 illustrates a serial data stream packet in accordance with anembodiment of the disclosure.

FIG. 6 illustrates a block diagram of a clock and data recoverydeserializer for a PLD in accordance with an embodiment of thedisclosure.

FIGS. 7-9 illustrate a Grey code oscillator implementation for a PLD inaccordance with an embodiment of the disclosure.

FIGS. 10-11 illustrate a Grey to binary converter implementation for aPLD in accordance with an embodiment of the disclosure.

FIGS. 12-15 illustrate block diagrams of circuitry implementing a datarecovery deserializer for a PLD in accordance with an embodiment of thedisclosure.

FIG. 16 illustrates a Grey Oscillator implementation for a PLD inaccordance with an embodiment of the disclosure.

FIG. 17 illustrates a block diagram of a clock and/or data recoverydeserializer for a PLD in accordance with an embodiment of thedisclosure.

FIG. 18 illustrates a block diagram of a timing circuit for a clockand/or data recovery deserializer in accordance with an embodiment ofthe disclosure.

FIG. 19 illustrates a Grey to binary converter for a timing circuit inaccordance with an embodiment of the disclosure.

FIG. 20 illustrates a block diagram of a calibration signal generatorfor a timing circuit in accordance with an embodiment of the disclosure.

FIG. 21 illustrates a block diagram of a flip flop for a calibrationsignal generator output in accordance with an embodiment of thedisclosure.

FIG. 22 illustrates a block diagram of a calibration circuit for a clockand/or data recovery deserializer in accordance with an embodiment ofthe disclosure.

FIG. 23 illustrates a block diagram of a decoder/decoder circuit for aclock and/or data recovery deserializer in accordance with an embodimentof the disclosure.

FIG. 24 illustrates a block diagram of a recovered data splitter 2310for a decoder in accordance with an embodiment of the disclosure.

FIG. 25 illustrates a block diagram of a word-aligned data splitter fora recovered data splitter in accordance with an embodiment of thedisclosure.

FIG. 26 illustrates a block diagram of a modulo 10 integrator for arecovered data splitter in accordance with an embodiment of thedisclosure.

FIG. 27 illustrates a method for operating a clock and/or data recoverydeserializer in accordance with an embodiment of the disclosure.

FIG. 28 illustrates a method for operating a clock and/or data recoverydeserializer in accordance with an embodiment of the disclosure.

Embodiments of the present disclosure and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

In accordance with various embodiments set forth herein, techniques areprovided to implement clock and/or data recovery circuitry substantiallywithin configurable (e.g., as opposed to dedicated) logic components ofa programmable logic device (PLD). For example, in some embodiments, aPLD includes a plurality of programmable logic blocks (PLBs), memoryblocks, digital signal processing blocks, input/output blocks, and/orother components that may be interconnected in a variety of ways toimplement a desired circuit design and/or functionality. A circuitdesign may be represented, at least in part, by a netlist, which candescribe components and connections therebetween in the design. Forexample, a user design may be converted into and/or represented by anetlist including set of PLD components (e.g., configured for logic,arithmetic, clocking, and/or other hardware functions) and associatedinterconnections available in a PLD. The netlist may be used to placecomponents and/or route connections for the design (e.g., using routingresources of the PLD) with respect to a particular PLD (e.g., using asimulation of the desired circuit design constructed from the netlist).

In general, a PLD (e.g., an FPGA) fabric includes various routingstructures and an array of similarly arranged logic cells arrangedwithin programmable function blocks (e.g., PFBs and/or PLBs). The goalin designing a particular type of PLD is to maximize functionality whileminimizing area, power, and delay of the fabric. Conventional clockand/or data recovery functionality (e.g., used to extract a clock signaland/or a data signal from a serial data stream, such as a single-endeddata stream transmitted without a separate clock signal) is typicallyimplemented by dedicated deserializer blocks that can employ a phaselocked loop or an interface to an accurate (e.g., low drift over time)clock and generally take up significant space and particularly limitedresources on a typical PLD, as well as dictate collateral timingconstraints (e.g., due to delay issues) throughout a user design, all ofwhich work to minimize the functionality of the PLD when used toimplement a design incorporating a deserializer block or blocks.

Embodiments of the present disclosure overcome these problems by usinggenerally configurable logic blocks to implement the entirety of thedeserializer (e.g., the clock and/or data recovery circuitry). Forexample, embodiments of the present disclosure use generallyconfigurable logic blocks in a PLD to implement a relatively inaccuratering type oscillator that can be used to calibrate recovery circuitry(e.g., also implemented in generally configurable logic blocks) to anincoming serial data stream that can then be used to recover a clocksignal and/or a data signal from the serial data stream. Because thedeserializer block can be implemented using generally configurable logicblocks, a user design incorporating embodiments of the presentdisclosure can generally be routed more easily, due to the addedconfiguration flexibility, and can incorporate significantly moredeserializer functionality than conventional techniques.

While the embodiments described herein present significant improvementsin the field of PLD utilization, such designs may also be used in custombuilt register transfer level (RTL) logic that can be implemented in ageneral integrated circuit and/or as its own type of dedicateddeserializer block in a PLD. Embodiments of the present design haveshown significant improvements in the ratio of performance to cost,power, and space utilization, both when implemented in a PLD or in RTLlogic for a customized IC. As such, embodiments of the presentdisclosure should not be viewed as generally limited only to PLDimplementations.

Referring now to the drawings, FIG. 1 illustrates a block diagram of aPLD 100 in accordance with an embodiment of the disclosure. In variousembodiments, PLD 100 may be implemented as a standalone device, forexample, or may be embedded within a system on a chip (SOC), other logicdevices, and/or other integrated circuit(s). PLD 100 (e.g., a fieldprogrammable gate array (FPGA), a complex programmable logic device(CPLD), a field programmable system on a chip (FPSC), or other type ofprogrammable device) generally includes input/output (I/O) blocks 102and logic blocks 104 (e.g., also referred to as programmable logicblocks (PLBs), programmable functional units (PFUs), or programmablelogic cells (PLCs)).

I/O blocks 102 provide I/O functionality (e.g., to support one or moreI/O and/or memory interface standards) for PLD 100, while programmablelogic blocks 104 provide logic functionality (e.g., look up table (LUT)based logic or logic gate array based logic) for PLD 100. Additional I/Ofunctionality may be provided by serializer/deserializer (SERDES) blocks150 and physical coding sublayer (PCS) blocks 152. PLD 100 may alsoinclude hard intellectual property core (IP) blocks 160 to provideadditional functionality (e.g., substantially predeterminedfunctionality provided in hardware which may be configured with lessprogramming than logic blocks 104).

PLD 100 may also include blocks of memory 106 (e.g., blocks of EEPROM,block SRAM, and/or flash memory), clock-related circuitry 108 (e.g.,clock driver sources, PLL circuits, DLL circuits, and/or feedlineinterconnects), and/or various routing resources (e.g., interconnectsand appropriate switching logic to provide paths for routing signalsthroughout PLD 100, such as for clock signals, data signals, or others)as appropriate. In general, the various elements of PLD 100 may be usedto perform their intended functions for desired applications, as wouldbe understood by one skilled in the art.

For example, certain I/O blocks 102 may be used for programming memory106 or transferring information (e.g., various types of user data and/orcontrol signals) to/from PLD 100. Other I/O blocks 102 include a firstprogramming port (which may represent a central processing unit (CPU)port, a peripheral data port, an SPI interface, and/or a sysCONFIGprogramming port) and/or a second programming port such as a joint testaction group (JTAG) port (e.g., by employing standards such as Instituteof Electrical and Electronics Engineers (IEEE) 1149.1 or 1532standards). In various embodiments, I/O blocks 102 may be included toreceive configuration data and commands (e.g., over one or moreconnections 140) to configure PLD 100 for its intended use and tosupport serial or parallel device configuration and information transferwith SERDES blocks 150, PCS blocks 152, hard IP blocks 160, and/or logicblocks 104 as appropriate.

In another example, routing resources (e.g., routing resources 180 ofFIG. 2) may be used to route connections between components, such asbetween I/O nodes of logic blocks 104. In some embodiments, such routingresources may include programmable elements (e.g., nodes where multiplerouting resources intersect) that may be used to selectively form asignal path for a particular connection between components of PLD 100.

It should be understood that the number and placement of the variouselements are not limiting and may depend upon the desired application.For example, various elements may not be required for a desiredapplication or design specification (e.g., for the type of programmabledevice selected).

Furthermore, it should be understood that the elements are illustratedin block form for clarity and that various elements would typically bedistributed throughout PLD 100, such as in and between logic blocks 104,hard IP blocks 160, and routing resources (e.g., routing resources 180of FIG. 2) to perform their conventional functions (e.g., storingconfiguration data that configures PLD 100 or providing interconnectstructure within PLD 100). It should also be understood that the variousembodiments disclosed herein are not limited to programmable logicdevices, such as PLD 100, and may be applied to various other types ofprogrammable devices, as would be understood by one skilled in the art.

An external system 130 may be used to create a desired userconfiguration or design of PLD 100 and generate correspondingconfiguration data to program (e.g., configure) PLD 100. For example,system 130 may store such configuration data to memory 134 and/ormachine readable medium 136, and/or provide such configuration data toone or more I/O blocks 102, memory blocks 106, SERDES blocks 150, and/orother portions of PLD 100. As a result, programmable logic blocks 104,various routing resources, and any other appropriate components of PLD100 may be configured to operate in accordance with user-specifiedapplications.

In the illustrated embodiment, system 130 is implemented as a computersystem. In this regard, system 130 includes, for example, one or moreprocessors 132 which may be configured to execute instructions, such assoftware instructions, provided in one or more memories 134 and/orstored in non-transitory form in one or more non-transitory machinereadable mediums 136 (e.g., which may be internal or external to system130). For example, in some embodiments, system 130 may run PLDconfiguration software, such as Lattice Diamond System Planner softwareavailable from Lattice Semiconductor Corporation to permit a user tocreate a desired configuration and generate corresponding configurationdata to program PLD 100.

System 130 also includes, for example, a user interface 135 (e.g., ascreen or display) to display information to a user, and one or moreuser input devices 137 (e.g., a keyboard, mouse, trackball, touchscreen,and/or other device) to receive user commands or design entry to preparea desired configuration of PLD 100. In some embodiments, user interface135 may be adapted to display a netlist, a component placement, aconnection routing, hardware description language (HDL) code, and/orother final and/or intermediary representations of a desired circuitdesign, for example.

FIG. 2 illustrates a block diagram of a logic block 104 of PLD 100 inaccordance with an embodiment of the disclosure. As discussed, PLD 100includes a plurality of logic blocks 104 including various components toprovide logic and arithmetic functionality, which can also be used toimplement one or more clock and/or data recovery deserializers ordeserializer blocks, as described herein.

In the example embodiment shown in FIG. 2, logic block 104 includes aplurality of logic cells 200, which may be interconnected internallywithin logic block 104 and/or externally using routing resources 180.For example, each logic cell 200 may include various components such as:a lookup table (LUT) 202, a mode logic circuit 204, a register 206(e.g., a flip-flop or latch), and various programmable multiplexers(e.g., programmable multiplexers 212 and 214) for selecting desiredsignal paths for logic cell 200 and/or between logic cells 200. In thisexample, LUT 202 accepts four inputs 220A-220D, which makes it afour-input LUT (which may be abbreviated as “4-LUT” or “LUT4”) that canbe programmed by configuration data for PLD 100 to implement anyappropriate logic operation having four inputs or less. Mode logic 204may include various logic elements and/or additional inputs, such asinput 220E, to support the functionality of various modes for logic cell200 (e.g., including various clock signal processing and/orfunctionality modes). LUT 202 in other examples may be of any othersuitable size having any other suitable number of inputs for aparticular implementation of a PLD. In some embodiments, different sizeLUTs may be provided for different logic blocks 104 and/or differentlogic cells 200.

An output signal 222 from LUT 202 and/or mode logic 204 may in someembodiments be passed through register 206 to provide an output signal233 of logic cell 200. In various embodiments, an output signal 223 fromLUT 202 and/or mode logic 204 may be passed to output 223 directly, asshown. Depending on the configuration of multiplexers 210-214 and/ormode logic 204, output signal 222 may be temporarily stored (e.g.,latched) in latch 206 according to control signals 230. In someembodiments, configuration data for PLD 100 may configure output 223and/or 233 of logic cell 200 to be provided as one or more inputs ofanother logic cell 200 (e.g., in another logic block or the same logicblock) in a staged or cascaded arrangement (e.g., comprising multiplelevels) to configure logic and/or other operations that cannot beimplemented in a single logic cell 200 (e.g., operations that have toomany inputs to be implemented by a single LUT 202). Moreover, logiccells 200 may be implemented with multiple outputs and/orinterconnections to facilitate selectable modes of operation, asdescribed herein.

Mode logic circuit 204 may be utilized for some configurations of PLD100 to efficiently implement arithmetic operations such as adders,subtractors, comparators, counters, or other operations, to efficientlyform some extended logic operations (e.g., higher order LUTs, working onmultiple bit data), to efficiently implement a relatively small RAM,and/or to allow for selection between logic, arithmetic, extended logic,and/or other selectable modes of operation. In this regard, mode logiccircuits 204, across multiple logic cells 202, may be chained togetherto pass carry-in signals 205 and carry-out signals 207, and/or othersignals (e.g., output signals 222) between adjacent logic cells 202, asdescribed herein. In the example of FIG. 2, carry-in signal 205 may bepassed directly to mode logic circuit 204, for example, or may be passedto mode logic circuit 204 by configuring one or more programmablemultiplexers. In some embodiments, mode logic circuits 204 may bechained across multiple logic blocks 104.

Logic cell 200 illustrated in FIG. 2 is merely an example, and logiccells 200 according to different embodiments may include differentcombinations and arrangements of PLD components. Also, although FIG. 2illustrates logic block 104 having eight logic cells 200, logic block104 according to other embodiments may include fewer logic cells 200 ormore logic cells 200. Each of the logic cells 200 of logic block 104 maybe used to implement a portion of a user design implemented by PLD 100.In this regard, PLD 100 may include many logic blocks 104, each of whichmay include logic cells 200 and/or other components which are used tocollectively implement the user design.

FIG. 3 illustrates a design process 300 for a PLD in accordance with anembodiment of the disclosure. For example, the process of FIG. 3 may beperformed by system 130 running Lattice Diamond software to configurePLD 100. In some embodiments, the various files and informationreferenced in FIG. 3 may be stored, for example, in one or moredatabases and/or other data structures in memory 134, machine readablemedium 136, and/or otherwise.

In operation 310, system 130 receives a user design that specifies thedesired functionality of PLD 100. For example, the user may interactwith system 130 (e.g., through user input device 137 and hardwaredescription language (HDL) code representing the design) to identifyvarious features of the user design (e.g., high level logic operations,hardware configurations, I/O and/or SERDES operations, and/or otherfeatures). In some embodiments, the user design may be provided in aregister transfer level (RTL) description (e.g., a gate leveldescription). System 130 may perform one or more rule checks to confirmthat the user design describes a valid configuration of PLD 100. Forexample, system 130 may reject invalid configurations and/or request theuser to provide new design information as appropriate.

In operation 320, system 130 synthesizes the design to create a netlist(e.g., a synthesized RTL description) identifying an abstract logicimplementation of the user design as a plurality of logic components(e.g., also referred to as netlist components). In some embodiments, thenetlist may be stored in Electronic Design Interchange Format (EDIF) ina Native Generic Database (NGD) file.

In some embodiments, synthesizing the design into a netlist in operation320 may involve converting (e.g., translating) the high-leveldescription of logic operations, hardware configurations, and/or otherfeatures in the user design into a set of PLD components (e.g., logicblocks 104, logic cells 200, and other components of PLD 100 configuredfor logic, arithmetic, or other hardware functions to implement the userdesign) and their associated interconnections or signals. Depending onembodiments, the converted user design may be represented as a netlist.

In various embodiments, synthesizing the design may include detecting aserial data stream input and/or a deserializer block configured togenerate a recovered data signal corresponding to a payload portion of aserial data stream (e.g., provided by the serial data stream input), forexample. In such embodiments, synthesizing such design may includesynthesizing the design into a plurality of PLD components configured toimplement a Grey code oscillator for the deserializer block that isconfigured to measure time periods between signal transitions in theserial data stream, as described herein, and at least one comparator forthe deserializer block that is configured to compare the measured timeperiods provided by the Grey code oscillator to one or more calibrationtime periods to generate the recovered data signal.

In some embodiments, synthesizing the design into a netlist in operation320 may further involve performing an optimization process on the userdesign (e.g., the user design converted/translated into a set of PLDcomponents and their associated interconnections or signals) to reducepropagation delays, consumption of PLD resources and routing resources,and/or otherwise optimize the performance of the PLD when configured toimplement the user design. Depending on embodiments, the optimizationprocess may be performed on a netlist representing theconverted/translated user design. Depending on embodiments, theoptimization process may represent the optimized user design in anetlist (e.g., to produce an optimized netlist).

In some embodiments, the optimization process may include optimizingrouting connections identified in a user design. For example, theoptimization process may include detecting connections with timingerrors in the user design, and interchanging and/or adjusting PLDresources implementing the invalid connections and/or other connectionsto reduce the number of PLD components and/or routing resources used toimplement the connections and/or to reduce the propagation delayassociated with the connections.

In operation 330, system 130 performs a mapping process that identifiescomponents of PLD 100 that may be used to implement the user design. Inthis regard, system 130 may map the optimized netlist (e.g., stored inoperation 320 as a result of the optimization process) to various typesof components provided by PLD 100 (e.g., logic blocks 104, logic cells200, embedded hardware, and/or other portions of PLD 100) and theirassociated signals (e.g., in a logical fashion, but without yetspecifying placement or routing). In some embodiments, the mapping maybe performed on one or more previously-stored NGD files, with themapping results stored as a physical design file (e.g., also referred toas an NCD file). In some embodiments, the mapping process may beperformed as part of the synthesis process in operation 320 to produce anetlist that is mapped to PLD components.

In operation 340, system 130 performs a placement process to assign themapped netlist components to particular physical components residing atspecific physical locations of the PLD 100 (e.g., assigned to particularlogic cells 200, logic blocks 104, clock-related circuitry 108, routingresources 180, and/or other physical components of PLD 100), and thusdetermine a layout for the PLD 100. In some embodiments, the placementmay be performed in memory on data retrieved from one or morepreviously-stored NCD files, for example, and/or on one or morepreviously-stored NCD files, with the placement results stored (e.g., inmemory 134 and/or machine readable medium 136) as another physicaldesign file.

In operation 350, system 130 performs a routing process to routeconnections (e.g., using routing resources 180) among the components ofPLD 100 based on the placement layout determined in operation 340 torealize the physical interconnections among the placed components. Insome embodiments, the routing may be performed in memory on dataretrieved from one or more previously-stored NCD files, for example,and/or on one or more previously-stored NCD files, with the routingresults stored (e.g., in memory 134 and/or machine readable medium 136)as another physical design file.

In various embodiments, routing the connections in operation 350 mayfurther involve performing an optimization process on the user design toreduce propagation delays, consumption of PLD resources and/or routingresources, and/or otherwise optimize the performance of the PLD whenconfigured to implement the user design. The optimization process may insome embodiments be performed on a physical design file representing theconverted/translated user design, and the optimization process mayrepresent the optimized user design in the physical design file (e.g.,to produce an optimized physical design file).

In some embodiments, the optimization process may include optimizingrouting connections identified in a user design. For example, theoptimization process may include detecting connections with timingerrors in the user design, and interchanging and/or adjusting PLDresources implementing the invalid connections and/or other connectionsto reduce the number of PLD components and/or routing resources used toimplement the connections and/or to reduce the propagation delayassociated with the connections.

Changes in the routing may be propagated back to prior operations, suchas synthesis, mapping, and/or placement, to further optimize variousaspects of the user design.

Thus, following operation 350, one or more physical design files may beprovided which specify the user design after it has been synthesized(e.g., converted and optimized), mapped, placed, and routed (e.g.,further optimized) for PLD 100 (e.g., by combining the results of thecorresponding previous operations). In operation 360, system 130generates configuration data for the synthesized, mapped, placed, androuted user design. In operation 370, system 130 configures PLD 100 withthe configuration data by, for example, loading a configuration databitstream into PLD 100 over connection 140.

FIG. 4 illustrates a schematic diagram of a clock and/or data recoverydeserializer 400 for a PLD in accordance with an embodiment of thedisclosure. As shown in the embodiment presented by FIG. 4, the generalschematic of clock and/or data recovery deserializer (e.g., deserializercircuit or block) 400 includes two asynchronously running Grey codeoscillators 420 and 422 providing timing signals to time respective lowand high level time periods of serial data stream 410. For example, eachof Grey code oscillators 420 and 422 may be implemented as oversamplingoscillators (e.g., relative to serial data stream 410) configured tomeasure time periods between signal transitions in serial data stream410 (e.g., between negative and adjacent positive signal transitions inserial data stream 410 for Grey code oscillator 420, and betweenpositive and adjacent negative signal transitions in serial data stream410 for Grey code oscillator 420).

Each Grey code oscillator 420 and 422 may be configured to increment aGrey code count between appropriate signal transitions in serial datastream 410 and provide such counts to calibration latches/storageregisters 440 and 442. Calibration signal 412 may be used to causestorage registers 440 and 442 to store calibration time periods (e.g.,measured by respective Grey code counts) corresponding to a trainingpreamble or other portion of serial data stream 410 (e.g., whenenabled), for example, or to pass payload time periods (e.g., alsomeasured by respective Grey code counts provided by Grey codeoscillators 420 and 422) along with the calibration time periods toblock 460. Clock and/or data recovery deserializer 400 may optionally beimplemented with a single Grey code oscillator that can be used to timeboth the high and the low time periods, as described herein.

In some embodiments, block 460 may be configured to compare measuredpayload time periods to calibration time periods and use the result ofsuch comparison to generate recovered data signal 480 and/or recoveredclock signal 482. For example, block 460 may be configured to generate asignal transition in recovered clock signal 482 upon a measured payloadtime period exceeding a corresponding calibration time period, and thento use the signal transition to sample serial data stream 410 togenerate recovered data signal 480. In other embodiments, block 460 maybe configured compare measured payload time periods to a number ofdifferent calibration time periods, for example, and generate recovereddata signal based such comparisons. More generally, embodiments of clockand/or data recovery deserializer 400 may be configured to recoverand/or decode a data signal from a serial data stream encoded accordingto a variety of different encoding schemes (e.g., a pulse widthmodulation encoding, a phase modulation encoding, a pulse width phasemodulation encoding, various bit depth encodings, and/or variable bitdepth encodings, for example), using an embodiment of Grey codeoscillator(s) 420 and/or 422 to measure time periods and/or other signalcharacteristics associated with the data and/or data encodingtransmitted by the serial data stream. Additional implementation detailsare provided in discussion of FIGS. 6-26.

FIG. 5 illustrates a serial data stream/packet 500 in accordance with anembodiment of the disclosure. As shown in FIG. 5, a typical serial datastream 500 includes a preamble 502 to indicate the beginning of serialdata stream 500, a payload portion 504 (e.g., the substantive data beingtransmitted by the serial data stream), and an end of packet portion 506to indicate the end of serial data stream 500/payload portion 504.Preamble 502 typically includes a training portion 512 with a knownsignal transition pattern and length that can be used to calibrate adeserializer/clock and/or data recovery deserializer, as describedherein. Start of packet portion 514 may include a known signaltransition pattern to indicate the beginning of payload portion 504. Forexample, clock and/or data recovery deserializer 400 may be configuredto use Grey code oscillators 420 and 422 to measure respective low andhigh time periods between appropriate signal transitions within trainingportion 512 and to store corresponding low and high calibration timeperiods in respective storage registers 440 and 442 for later use byblock 460.

Also shown in FIG. 5 are positive signal transition 520 (e.g., from lowto high), negative signal transition 522 (e.g., from high to low), hightime period 524 (e.g., the time period between a positive signaltransition and an adjacent negative signal transition), and low timeperiod 526 (e.g., the time period between a negative signal transitionand an adjacent positive signal transition). Additionally shown is datacell 528, which may be a length of serial data stream 500 correspondingto the width of a single data bit and/or the width of two adjacentsignal transitions in training portion 512.

FIG. 6 illustrates a block diagram of a clock and data recoverydeserializer 600 for a PLD in accordance with an embodiment of thedisclosure. In general, clock and data recovery deserializer 600operates similar to clock and data recovery deserializer 400 of FIG. 4,but includes additional functionality to reduce a risk of race and/orother timing issues. In general, clock and data recovery deserializer600 is configured to receive a serial data stream/input 610, measuretime periods between signal transitions corresponding to serial datastream 610, and generate a recovered clock signal/output 682 and arecovered data signal/output 680, and may be implemented entirely withgenerally configurable resources of a PLD.

As shown in FIG. 6, clock and data recovery deserializer 600 includescalibration signal generators 612 and 615, asynchronous oversamplingGrey code oscillators 620, low and high Grey code converters 640 and642, calibration storage registers 644, clock recovery circuit 660, anddata recovery circuit 670. Calibration signal generators 612 and 615 maygenerally be configured to receive a raw serial data stream (e.g.,direct from input 610) and generate and provide a calibration serialdata stream to Grey code oscillators 620 while enabled (e.g., bycalibration enable signal 611). For example, when calibration enablesignal 611 is high, divider block 613 of calibration signal generator612 may be configured to generate a calibration serial data stream witha period that is four times longer than the period of serial data stream610, and multiplexers 617 and 618 may be configured to pass thegenerated calibration serial data stream on to Grey code oscillators620.

Calibration enable signal 611 may be enabled/disabled upon detecting apreamble or training portion of serial data stream 610 and/or a start ofpacket portion of serial data stream 610. Calibration signal generator615, as shown in FIG. 6, may be configured simply to pass a trainingportion of serial data stream 610 (e.g., corresponding to calibrationenable signal 611 being low). In some embodiments, calibration signalgenerator 615 may be configured to provide at least a single clock widththat is to occur after calibration enable signal 611 is disabled butbefore the start of a payload portion of serial data stream 610.

In other embodiments, other calibration signal generators configured togenerate other calibration serial data streams may be included in clockand data recovery deserializer 600. In general, such calibration serialdata streams may be characterized by a calibration period correspondingto a whole number multiple of a clock period of the raw serial datastream (e.g., of a training portion of serial data stream 610).Corresponding calibration time periods/binary counts (e.g., stored instorage registers 644) may be approximately half the full calibrationperiod. In various embodiments, calibration signal generators 612 and615 may be configured to detect a training portion in a preamble ofserial data stream 610 and/or generate one or more calibration serialdata streams based, at least in part, on the training portion of serialdata stream 610.

Asynchronous oversampling Grey code oscillators 620 may include one ormore Grey code oscillators (e.g., low Grey code oscillator 621 and highGrey code oscillator 622) configured to measure time periods (e.g.,calibration, payload, high, low, and/or other time periods) betweensignal transitions in a serial data stream (e.g., in a calibration orraw serial data stream, and/or in a training portion or a payloadportion of a serial data stream) provided to or generated by variouselements of clock and data recovery deserializer 600. Each Grey codeoscillator 621 and 622 may be configured to increment a Grey code countbetween signal transitions in a serial data stream, and as such, eachGrey code oscillator should be implemented so as to increment its Greycode count multiple times during a half period of a clock cycle of (raw)serial data stream 610, so as to provide sufficient resolution torecover the corresponding clock and/or data signals.

In particular, low Grey code oscillator 621 may be configured toincrement a first Grey code count from zero between negative andadjacent positive signal transitions in serial data stream 610 and/or acorresponding calibration serial data stream (e.g., a low portion ofsuch streams), and Grey code oscillator 622 may be configured toincrement a second Grey code count, asynchronously relative to the firstGrey code count, from zero between positive and adjacent negative signaltransitions in serial data stream 610 and/or a corresponding calibrationserial data stream (e.g., a high portion of such streams). The timing ofstart, stop, and reset of each of Grey code oscillators 621 and 622 maybe controlled by sample timing circuitry 623, 625, and/or 625, forexample, along with appropriate signal transitions in serial data stream610 and/or a corresponding calibration serial data stream (e.g.,provided by multiplexers 616 and 617 to respective Grey code oscillators621 and 622).

In various embodiments, sample timing circuitry 623, 625, and/or 625 mayadvantageously include elements coupled between Grey code oscillators620 (e.g., Grey code oscillator 621 and Grey code oscillator 622), Greycode converters 640 and 642, and/or storage registers 644, so as tofacilitate proper timing between operation of the various elementswithout incurring race conditions or other timing issues. For example,as can be seen in FIG. 6, AND gate 623 requires Grey code oscillator 622reach a minimum Grey code count (e.g., a pattern of outputs c1 and b1)before resetting Grey code oscillator 621 (e.g., by providing a highsignal to input f of Grey code oscillator 621), and AND gate 624requires Grey code oscillator 621 reach a minimum Grey code count beforeresetting Grey code oscillator 622. Also, traces 625 require a Grey codecount of Grey code oscillator 621 reach a minimum Grey code count beforehigh calibration time periods measured by Grey code oscillator 622 arestored in storage registers 644, and require a Grey code count of Greycode oscillator 622 reach a minimum Grey code count before lowcalibration time periods measured by Grey code oscillator 621 are storedin storage registers 644, as shown. In some embodiments, the minimumGrey code counts initiating resets and storage may be identical. Greycode oscillators 621 and 622 may be configured to start incrementingtheir respective Grey code counts based on signal transitions in signalsprovided to inputs e of Grey code oscillators 621 and 622 (e.g.,calibration/serial data streams provided by multiplexers 616 and 617).

Grey code converters 640 and 642 may be configured to convert Grey codecounts provided by Grey code oscillators 620 into a different format,such as binary counts, as shown. Such binary counts may represent a highor low time period measured by Grey code oscillators 620. For example,Grey code converters 640 and 642 may be configured to convert Grey codecounts provided by respective low/high Grey code oscillators 621/622 tocorresponding low/high binary counts. In particular, Grey code converter640 may be configured to convert a Grey code count providedapproximately at a positive signal transition in a signal provided toinput e of Grey code oscillator 621 to a low binary count correspondingto a low time period (e.g., a calibration, training, and/or payload timeperiod) between a negative and an adjacent positive signal transition inthe signal provided to input e of Grey code oscillator 621. Similarly,Grey code converter 642 may be configured to convert a Grey code countprovided approximately at a negative signal transition in a signalprovided to input e of Grey code oscillator 622 to a high binary countcorresponding to a high time period between a positive and an adjacentnegative signal transition in the signal provided to input e of Greycode oscillator 622. Such low and high binary counts may correspond tolow and high calibration and/or payload binary counts, for example.

In the embodiment presented by FIG. 6, each Grey code converters 640/642includes respective Grey to binary blocks 650/655 coupled to theirrespective Grey code oscillators and binary counters 651/656 coupled tothe most significant bit outputs d0/d1 of their respective Grey codeoscillators. As shown in FIG. 6, outputs d0 and d1 of Grey codeoscillators 621 and 622 correspond to the base frequency (e.g., lowestfrequency) outputs of Grey code oscillators 621 and 622, and as such,transitions in those outputs can be counted by a conventional binarycounter without risk of generating a race condition or other timingissue at the inputs of storage registers 644 and/or various clock/datarecovery circuitry further along the signal propagation paths in clockand data recovery deserializer 600. Moreover, binary counters 651/656allow Grey code oscillators 621/622 to measure time periods greater thanthe maximum Grey code count achievable by Grey code oscillators 621/622,by incrementing as each Grey code oscillator passes through its maximumGrey code count. Grey code converters 640/642 each concatenate the mostsignificant bits of the binary count (e.g., the slowest changing bits)provided by binary counters 651/656 with the least significant bits ofthe binary count (e.g., the fastest changing bits) provided by Grey tobinary blocks 650/655 and then provide the resulting binary counts tostorage registers 644.

In general, storage registers 644 may be configured to store datarepresentative of time periods (e.g., calibration time periods, trainingtime periods, payload time periods, and/or other time periods) measuredby Grey code oscillators 620, and provide the stored time periods toclock recovery circuit 660 and/or data recovery circuit 670 (e.g., tocomparators and/or other circuit elements within circuits 660 and/or670). More particularly, storage registers 644 may be configured tostore high and low binary counts (e.g., calibration binary counts,and/or other binary counts) corresponding to high and low time periodsmeasured by Grey code oscillators 620.

For example, as shown in FIG. 6, storage registers 652 and 657 may beconfigured to store respective low and high calibration binary countscorresponding to low and high time periods of a calibration signalgenerated by calibration signal generator 615 (e.g., CAL1), and storageregisters 653 and 658 may be configured to store respective low and highcalibration binary counts corresponding to low and high time periods ofa calibration signal generated by calibration signal generator 612(e.g., CAL4). In various embodiments, storage registers 644 may includeadditional or a different number of storage registers 652, 653, 657,658, and/or a different selection of latching logic (e.g., the AND gateslinked to their respective storage registers in storage registers 644),for example, to store additional and/or different binary countscorresponding to additional or different time periods, such as thoseassociated with additional or different calibration serial data streams,payload portions of a serial data stream, and/or others. Moreover, suchlatching logic may be configured to latch storage registers 644according to a different selection of sample times (e.g., as dictated,at least in part, by sample timing circuitry/traces 625 and/or serialdata stream 610, as shown).

Additionally as shown in FIG. 6, in some embodiments, storage registers644 may be configured to perform various operations on the binary countsas they are stored and/or as they are provided to other elements ofclock and data recovery deserializer 600. In particular, storageregisters 653 and 658 may be configured to divide a binary countprovided to those registers by 4 (e.g., using a bit shift operation) soas to store and/or provide a binary count that is an average low or hightime period corresponding to a single high or low time period of atraining portion/clock signal of serial data stream 610, for example,averaged over four consecutive low or high time periods of the trainingportion/clock signal of serial data stream 610. In some embodiments, theCAL4 calibration time periods with be stored in storage registers 644 atthe end of each training portion of serial data stream 610. Logic at theoutput of storage registers 644 may be configured to provide initialdelay binary counts to determine a center of a beginning pulse in serialdata stream 610.

As also shown in FIG. 6, clock and data recovery deserializer 600 mayinclude output multiplexers 646 configured to provide high/lowcalibration time periods/binary counts and/or high/low payload timeperiods/binary counts to clock recovery circuit 660 and/or data recoverycircuit 670, for example, which may be controlled by the instanthigh/low state of serial data stream 610. Once calibration signalgenerators 612 and 615 are disabled, the values in storage registers 646are stable, and only the non-calibration time period output N (e.g.,which may be a payload time period output) is updated as serial datastream 610 is processed by clock and data recovery deserializer 600.

Clock recovery circuit 660 may include at least one comparator (e.g.,comparator 665) and be configured to receive at least one calibrationbinary count (e.g., high or low, from storage registers 644) and binarycounts (e.g., from storage registers 644 and/or directly from Grey codeconverters 640 and/or 642, which may be payload binary counts) andgenerate recovered clock signal 682 corresponding to serial data stream610. For example, as shown in FIG. 6, recovered clock signal 682 may bebased, at least in part, on a change in the output state of comparator665. In some embodiments, comparator 665 may be configured to comparemeasured payload time periods (e.g., signals N provided to input A ofcomparator 665) to a calibration time period (e.g., which may be a basecalibration time period) and initiate a recovered clock signaltransition when a measured payload time period exceeds the calibrationtime period.

To recover a base clock corresponding to serial data stream 610 (e.g.,the highest frequency for signal transitions in serial data stream 610,typically presented in a training portion of serial data stream 610),clock recovery circuit 660 may include multiplexer 662, latch 663, andintegrator 664 configured to determine a high/low base calibration timeperiods (e.g., corresponding to a high/low base clock time periods) andprovide the base calibration time periods to comparator 665. As shown inthe embodiment presented by FIG. 6, clock recovery circuit 660 mayinclude additional logic (e.g., latches 661 and 666, and register 668)to help stabilize recovered clock signal 682 (e.g., with respect tocalibration time periods stored in latches 652 and 653, or in latches657 and 658) and/or to generate a double data rate version of recoveredclock signal 682. A shown, latch 663 may be reset substantially atsignal transitions in serial data stream 610 as detected by resetgenerator 618.

In FIG. 6, data recovery circuit 670 is configured to receive recoveredclock signal 682 (e.g., as provided by latch 666) and serial data stream610 (e.g., which may be propagated through a known delay as shown) andgenerate recovered data signal 680 corresponding to serial data stream610, which may be based, at least in part, on recovered clock signal 682and serial data stream 610, as shown. In particular, data recoverycircuit 670 may include register 672 configured to receive serial datastream 610 and periodically provide stored portions of serial datastream 610 as recovered data signal 680, as dictated by signaltransitions in recovered clock signal 682. In some embodiments, sucharrangement may be used to sample the center of each bit cell of serialdata stream 610.

More generally, data recovery circuit 670 may be configured to generaterecovered data signal 680 corresponding to a payload portion of serialdata stream 610 by, at least in part, relying on the comparison ofmeasured payload time periods (e.g., measured/provided by Grey codeoscillators 620) to one or more calibration time periods, which, asshown in FIG. 6, may be performed by clock recovery circuitry 660. Forexample, data recovery circuit 670 may be configured to generaterecovered data signal 680 by sampling a payload portion of serial datastream 610 at recovered clock signal transitions in recovered clocksignal 682. Other embodiments of clock and data recovery deserializer600 may omit clock recovery circuit 660 and instead use one or morecomparators implemented within data recovery circuit 670 to generatedata recovery signal 680, as described herein. Optionally, clock anddata recovery deserializer 600 may include a decoder configured toconvert recovered data signal 680 to a differently encoded or formatteddata signal, including converting 8b10b encoded data back into eight bitencoded data and/or parallel data signals, as described herein.

FIGS. 7-9 illustrate Grey code oscillator implementations for a PLD inaccordance with an embodiment of the disclosure. For example, FIG. 7includes a table 700 illustrating how a Grey code count of a Grey codeoscillator (e.g., Grey code oscillators 621 and 622) can be incrementedfrom zero (at the top of table 700) to a maximum Grey code count (e.g.,corresponding to a decimal count of 15) for a four bit Grey codeoscillator. Notably, at each transition in the incremental count, onlyone bit changes state. This is particularly advantageous at high countrates because it helps to eliminate risk of race conditions and/or othertiming issues associated with multiple bits changing states during asingle increment and timing the sampling or counting of such statechanges. Moreover, as noted herein, the most significant bit d changesthe slowest throughout the increment, though it and bit c effectivelyhave the same frequency as the Grey count is allowed to wrap from 15back to zero (e.g., from 1000 back to 0000).

FIG. 8 shows an embodiment of Grey code oscillator 621 that can beimplemented entirely within a single programmable logic block 104 (e.g.,eight locally linked programmable logic cells 200), using two chained4-LUTs per equation in logic 802. The benefit of implementing suchfreely oscillating oscillator entirely within a PLB is that each PLB ina PLD may linked relatively closely to each other and require relativelylittle routing resources 180 to, for example, chain individual 4-LUTs inadjacent PLCs, which allows Grey code oscillator 621 to oscillate orincrement at approximately the maximum propagation speed supported bythe underlying PLD, thereby maximizing the performance of Grey codeoscillator 621 and increasing the performance of clock and data recoverydeserializer 600 and the maximum recoverable serial data streamfrequency/bit rate/data rate. Similarly, FIG. 9 shows an embodiment ofGrey code oscillator 622 that can be implemented entirely within asingle programmable logic block 104 (e.g., eight locally linkedprogrammable logic cells 200), using two chained 4-LUTs per equation inlogic 902, and it's implementation benefits from similar advantages interms of performance and efficient use of PLD resources.

In general, Grey code oscillators 621 and 622 may be implemented asripple style Grey code oscillators with operating frequencies a minimumof approximately five times an expected maximum data rate of serial datastream 610. The exact frequencies for either or both Grey codeoscillators 621 and 622 do not need to be set, accurate, or known,because each oscillator will be effectively synchronized to serial datastream 610. Moreover, stability of their respective frequencies, eitherto themselves or to each other, is generally not required because thefrequencies may be re-synchronized for every serial data stream packet.For example, Grey code oscillators 621 and 622 may be synchronized withtransitions between low and high levels of serial data stream 610 duringa training portion of serial data stream 610. The training portion canbe as short as 4 data cells including an alternating one-zero sequence,but is typically approximately 50 data cell in length.

FIGS. 10-11 illustrate a Grey to binary converter implementation for aPLD in accordance with an embodiment of the disclosure. For example,FIG. 10 includes a table 1000 illustrating how a Grey code countprovided by a Grey code oscillator (e.g., Grey code oscillators 621 and622) can be converted to a binary count for a four bit Grey codeoscillator. FIG. 11 shows an embodiment of Grey to binary block 650 thatcan be implemented according to a limited number of logic elements 1102,which may include three cross linked XOR logic gates as shown. Forexample, logic 1102 may be implemented by three chained 4-LUTs (e.g.,corresponding to three linked PLCs), which may be implemented entirelywithin a PLB of a PLD, with benefits similar to those discussed withreference to Grey code oscillator implementations described in FIGS.7-9.

Embodiments of clock and data recovery deserializer 600 may be used torecover clock and/or data from serial data streams from 10-50 Mbps, forexample, and/or approaching serial data streams of 100 Mbps. Such ratesare achievable by PLD fabrics capable of supporting signals transiting achain of six LUTs at approximately 10 MHz rates or better, for example.As understood by one in the art, such rates are significantly dependentupon the process and techniques used to fabricate the underlying PLDfabric, for example, or upon processes and techniques used to fabricatean underlying IC (e.g., in embodiments where clock and data recoverydeserializer 600 is implemented in RTL logic). Embodiments providebenefits over conventional techniques, regardless of the underlying PLDor RTL logic fabric, in terms of relative performance per cost, powerusage, and/or space utilization.

FIGS. 12-15 illustrate block diagrams of circuitry implementing a datarecovery deserializer 1200 for a PLD in accordance with an embodiment ofthe disclosure. In particular, data recovery deserializer 1200 generallydiffers from clock and data recovery deserializer 600 of FIG. 6 in thatit uses a single freely running Grey code oscillator to measure bothhigh and low time periods of serial data streams (e.g., a calibrationserial data stream generated by calibration signal generator 612 and/orserial data stream 610), and it omits clock recovery circuit 660 andinstead relies on multiple comparators embedded within data recoverycircuit 1264 of FIGS. 14 and 1266 of FIG. 15, along with additionallogic, to generate recovered data signal 1280. Similar to clock and datarecovery deserializer 600 of FIG. 6, data recovery deserializer 1200 maybe implemented entirely with generally configurable resources of a PLD.In general, data recovery deserializer 1200 is configured to receiveserial data stream/input 610, measure time periods between signaltransitions corresponding to serial data stream 610 using Grey codeoscillator 1222, and generate recovered data signal/output 1280.

As shown in FIGS. 12-15, data recovery deserializer 1200 includescalibration signal generator 612, oversampling Grey code oscillator1222, Grey code counter 1242, low/high Grey count storage registers 1252and 1257, Grey code converters 650 and 655 (e.g., Grey to binary blocks650 and 655), time period logic block 1260, storage register 1362, and adata recovery circuit including data recovery circuit portions 1264,1266, logic block 1267, registers 1272 and 1273, and multiplexer 1274.In general operation, data recovery deserializer 1200 initiates Greycode oscillator 1222 incrementing its Grey code count either before orduring a training portion of serial data stream 610, and calibrationenable signal 611 is driven high to provide a calibration serial datastream from multiplexer 1217 corresponding to the training portion ofserial data stream 610.

During this phase of operation, signal transitions in the calibrationserial data stream are used to store corresponding low and high Greycode counts in respective registers 1252 and 1257, which are thenprovided to respective Grey to binary blocks 650 and 655 in order toconvert the Grey code counts to corresponding binary counts. Time periodlogic block 1260 determines the difference between the low and highbinary counts in order to determine a corresponding calibration timeperiod/binary count between adjacent transitions in the calibrationserial data stream, and the calibration time period/binary count isstored in storage register 1362. The calibration time period/binarycount is then provided to various comparators 1464, 1466, 1568, 1570,and, 1573, and integrators 1465, 1566, 1567, 1569, 1571, and 1572,within data recovery circuit portions 1264 and 1266.

Once the calibration phase is over, signal transitions in a payloadportion of serial data stream 610 are used to store corresponding lowand high Grey code counts in respective registers 1252 and 1257, whichare then provided to respective Grey to binary blocks 650 and 655 inorder to convert the Grey code counts to corresponding binary counts.Time period logic block 1260 determines the difference between the lowand high binary counts in order to determine a corresponding payloadtime period/binary count between adjacent transitions in the payloadportion of serial data stream 610, and the payload time period/binarycount is provided to the various comparators and integrators in datarecovery circuit portions 1264 and 1266, as shown.

In the embodiment shown in FIGS. 12-15, the various comparators andintegrators in recovery circuit portions 1264 and 1266 are configured todetect one of five possible data patterns (e.g., either high or low)expected in the payload portion of serial data stream 610 by changing anoutput state of the comparator when a compared payload timeperiod/binary count exceeds a corresponding calibration timeperiod/binary count and/or data pattern time period/binary count. Suchdata patterns may be chosen to generally correspond to any payload timeperiod/binary count measured by Grey code oscillator 1222 and providedin binary form by time period logic block 1260. As shown in logic 1268for logic block 1267, the state of comparator output p1 may be inferredbased on the remaining comparator outputs p2, p3, p4, and p5. Logicblock 1267 then provides the detected data pattern in storage register1272 or 1273, depending on the corresponding low or high state of serialdata stream 610, and the data patterns are concatenated and/or output bymultiplexer 1274 as recovered data signal 1280. As such, recovered datasignal 1280 may be based, at least in part, on a change in an outputstate of at least one of the comparators in recovery circuit portions1264 and 1266. In some embodiments, recovered data signal 1280 may beprovided to a decoder to convert recovered data signal 1280 to a desiredencoding or data signal format, as described herein.

In the embodiment shown in FIGS. 12-15, Grey code counter 1242 isimplemented as a logic block configured to count high to low transitionsin the most significant bit output of Grey code oscillator 1222 usingGrey code. This implementation is used to help eliminate race conditionsand/or other timing issues (e.g., at registers 1252 and 1257) that mightotherwise be caused by incremental counting using a binary code.

While data recovery circuit portions 1264, 1266, logic block 1267,registers 1272 and 1273, and multiplexer 1274 are configured to detectspecific data patterns in the payload portion of serial data stream 610,in other embodiments, data recovery deserializer 1200 may instead beimplemented with alternative data recovery circuit elements configuredto detect other data patterns and/or another number of data patterns,for example. In some embodiments, data recovery deserializer 1200 may beimplemented with a clock recovery circuit and data recovery circuitsimilar to those presented in FIG. 6. In other embodiments, datarecovery deserializer 1200 may be implemented with two Grey codeoscillators, similar in arrangement to those presented in FIG. 6, and beconfigured with separate data recovery circuit portions configured todetect data patterns corresponding to low and high payload binary countsseparately from each other. Such embodiments benefit from the racecondition elimination benefits and/or other timing issue benefitsdescribed with reference to the two Grey code oscillator circuitry andassociated sample timing circuitry described with reference to FIG. 6.

FIG. 16 illustrates a Grey Oscillator implementation for a PLD inaccordance with an embodiment of the disclosure. In particular, FIG. 16shows an embodiment of Grey code oscillator 1222 that can be implementedentirely within half a single programmable logic block 104 (e.g., fourlocally linked programmable logic cells 200), using one 4-LUT perequation in logic 1602. The benefit of implementing such freelyoscillating oscillator entirely within a PLB is that each PLB in a PLDmay linked relatively closely to each other and require relativelylittle routing resources 180 to, for example, chain individual 4-LUTs inadjacent PLCs, which allows Grey code oscillator 1222 to oscillate orincrement at approximately the maximum propagation speed supported bythe underlying PLD, thereby maximizing the performance of Grey codeoscillator 1222 and increasing the performance of data recoverydeserializer 1200 and the maximum recoverable serial data streamfrequency/bit rate/data rate. Moreover, such implementation provided forrelatively efficient use of PLD resources.

FIG. 17 illustrates a block diagram of a clock and/or data recoverydeserializer 1700 for a PLD in accordance with an embodiment of thedisclosure. In particular, clock and/or data recovery deserializer 1700generally differs from clock and data recovery deserializer 600 of FIG.6 and data recovery deserializer 1200 of FIG. 12 in that itsfunctionality is relatively pipelined, it omits clock recovery circuit660, it uses two separate series of comparators 1730-1738 and 1740-1746to generate separate high and low portions of a recovered data signal(e.g., output by registers 1750 and 1752), and it includes a decoder1770 configured to decode an encoded form of the recovered data signal(e.g., an 8b10b encoded recovered data signal) by converting the encodedrecovered data signal into a parallel eight bit recovered data signal.Similar to deserializers 600 and 1200, clock and/or data recoverydeserializer 1700 may be implemented entirely with generallyconfigurable resources of a PLD.

In general, clock and/or data recovery deserializer 1700 is configuredto receive serial data stream/input 1709 at timing circuit 1710,generate calibration and payload time periods at timing circuit 1710,store the calibration time periods within calibration circuit 1720,compare pairs of adjacent low and high payload time periods to variouscalibration time periods and/or data patterns at comparators 1730-1738and 1740-1746, store a corresponding encoded recovered data signal inregisters 1750 and 1752, and decode the encoded recovered data signal toprovide decoded recovered data signal 1772 at an output of decoder 1770.

As shown in FIG. 17, clock and/or data recovery deserializer 1700includes timing circuit 1710, calibration circuit 1720, comparators1730-1738 and 1740-1746, low/high storage registers 1750 and 1752, andoptional decoder 1770. In general operation, timing circuit 1710receives serial data stream 1709, detects a training portion of serialdata stream 1709 (e.g., or assumes the beginning of serial data stream1709 is the training portion), enters a calibration phase of operation(e.g., by driving one or more corresponding calibration enable signalshigh), measures one or more calibration time periods (e.g., low and highcalibration time periods for one or more different length calibrationserial data stream periods, such as signal periods corresponding to 2,3, 4, and 5 data cells of serial data stream 1709), and provides themeasured calibration time periods (e.g., in the form of binary counts)to calibration circuit 1720 for storage in a number of correspondingstorage registers. Calibration circuit 1720 receives and stores thecalibration time periods and may be configured to combine the variouscalibration time periods according to expected data patterns in payloadtime periods of a payload portion of serial data stream 1790 and providevarious calibration time periods and/or data pattern time periods tocomparators 1730-1738 and 1740-1746.

Timing circuit 1710 may then detect a start of packet portion of serialdata stream 1709 (or, in some embodiments, simply exit the calibrationphase of operation when the calibration phase completes bymeasuring/determining all the desired calibration/data pattern timeperiods), exit the calibration phase of operation (e.g., by drivingvarious calibration enable signals low), measure pairs of adjacent lowand high payload time periods (e.g., low and high payload time periodsfor a payload portion of serial data stream 1709), and provide theadjacent measured payload time periods (e.g., in the form of binarycounts) to comparators 1730-1738 and 1740-1746, as shown. Comparators1730-1738 and 1740-1746 may be configured to compare the measuredpayload time periods to the calibration/data pattern time periodsprovided by calibration circuit 1720 and store the resulting respectivelow and high portions of the recovered data signal in respectiveregisters 1750 and 1752. Optionally, decoder 1770 may then receive thelow and high portions of an encoded recovered data signal, decode theencoded recovered data signal into a desired recovered data signalencoding and/or format. In some embodiments, decoder 1770 may beconfigured to detect a beginning of a payload portion of serial datastream 1709 (e.g., a comma encoded within serial data stream 1709 at thebeginning of the payload portion) and only begin to provide decodedrecovered data signal 1772 after the beginning of the payload portion isdetected. In a particular embodiment, decoder 1770 may be configured todecode an 8b10b encoded recovered data signal into eight bit parallelformat recovered data signal 1772, as shown. In various embodiments,decoder 1770 and/or other elements of clock and/or data recoverydeserializer 1700 may be configured to generate a recovered clock signalbased, at least in part, on serial data stream 1709 and/or one or morecalibration time periods measured by timing circuit 1710.

In a specific embodiment, where serial data stream 1709 is an 8b10bencoded serial data stream, comparators 1730-1738 may be configured togenerate a low portion of a recovered encoded data signal by, at leastin part, detecting when a low payload time period measured by timingcircuit 1709 is roughly equivalent to two, three, four, or five datacell time periods (a low payload time period roughly equivalent to onedata cell time period is inferred by all the outputs of comparators1730-1738 being zero), where larger low payload time periods are notgenerated by the expected encoding of serial data stream 1709.Similarly, in such specific embodiment, comparators 1740-1748 may beconfigured to generate a high portion of a recovered encoded data signalby, at least in part, detecting when a high payload time period measuredby timing circuit 1709 is roughly equivalent to two, three, four, orfive data cell time periods (a high payload time period roughlyequivalent to one data cell time period is inferred by all the outputsof comparators 1740-1748 being zero), where larger high payload timeperiods are not generated by the expected encoding of serial data stream1709.

More generally, in other embodiments, clock and/or data recoverydeserializer 1700 may include a different number of comparators1730-1738 and/or 1740-1748, calibration circuit 1720 may generatedifferent combinations of calibration time periods and/or according todifferent expected data patterns, and/or timing circuit 1710 may measureand generate different calibration time periods, for example, accordingto a known encoding of serial data stream 1709. Moreover, in otherembodiments, serial data stream 1719 may be encoded according to avariety of different encoding schemes, such as a pulse width modulationencoding, a phase modulation encoding, a pulse width phase modulationencoding, other bit depth encodings, and/or variable bit depthencodings, for example, and elements of clock and/or data recoverydeserializer 1700, including decoder 1770, may be modified to recoverand/or decode a data signal from such serial data stream using anembodiment of Grey code oscillator(s) 621, 622, and/or 1222 to measuretime periods and/or other signal characteristics associated with thedata transmitted by the serial data stream.

FIG. 18 illustrates a block diagram of timing circuit 1710 for clockand/or data recovery deserializer 1700 in accordance with an embodimentof the disclosure. As shown in FIG. 18, timing circuit 1710 includescalibration signal generator 1810, reset generator 1880, low and highGrey code oscillators 621 and 622, a low Grey code converter includingGrey to binary block 1850 and binary counter 1851, a high Grey codeconverter including Grey to binary block 1855 and binary counter 1856,low and high storage registers 1860 and 1862, and sample timingcircuitry including logic blocks 1823, 1824, 1870, 1872, and 1874.Calibration signal generator 1810 may be configured to receive serialdata stream 1709 and generate various corresponding calibration serialdata streams and/or pass through serial data stream 1709 as serial datastream es, as described herein. In general operation, the Grey codeoscillators, Grey code converters, and sample timing circuitry of timingcircuit 1710 operate similarly to similar elements described withreference to deserializer 600 in FIG. 6.

For example, the sample timing circuity identified in FIG. 18 (e.g.,logic blocks 1870, 1872, 1874, 1823, and/or 1824) may be configured tocontrol the timing of start, stop, and reset of each of Grey codeoscillators 621 and 622, for instance, and/or storage of low and hightime periods (e.g., in the form of binary counts) in respective low/highstorage registers 1860 and 1862, according to internal clock signal CLK(e.g., generated by logic blocks 1870, 1872, and 1874) and serial datastream es generated by calibrate signal generator 1710. Logic blocks1823 and 1824 may be configured to reset binary counters 1850 and 1856according to internal clock signal CLK and serial data stream es. Binarycounters 1851 and 1856 may each be implemented with an additional outputconfigured to generate an internal reset signal RST when combinedaccording to reset signal generator 1880, as shown. Such internal resetsignal RST may be provided to calibration signal generator 1810, asshown.

In various embodiments, the sample timing circuity identified in FIG. 18(e.g., logic blocks 1870, 1872, 1874, 1823, and/or 1824) mayadvantageously include elements coupled between Grey code oscillator 621and Grey code oscillator 622, Grey code converters (e.g., Grey to binaryblock 1850 and binary counter 1851, and Grey to binary block 1855 andbinary counter 1856), and/or storage registers 1860 and 1862, so as tofacilitate proper timing between operation of the various elementswithout incurring race conditions or other timing issues.

For example, as can be seen in FIG. 18, logic blocks 1870-1874 requireGrey code oscillator 622 reach a minimum Grey code count (e.g., apattern of outputs al and b1) before resetting Grey code oscillator 621(e.g., by providing a high CLK signal to input f of Grey code oscillator621), and logic blocks 1870-1874 require Grey code oscillator 621 reacha minimum Grey code count before resetting Grey code oscillator 622.Also, logic blocks 1870-1874 require a Grey code count of Grey codeoscillator 621 reach a minimum Grey code count before high calibrationtime periods measured by Grey code oscillator 622 are stored in storageregister 1862, and require a Grey code count of Grey code oscillator 622reach a minimum Grey code count before low calibration time periodsmeasured by Grey code oscillator 621 are stored in storage register1860, as shown. In some embodiments, the minimum Grey code countsinitiating resets and storage may be identical. Grey code oscillators621 and 622 may be configured to start incrementing their respectiveGrey code counts based on signal transitions in signals provided toinputs e of Grey code oscillators 621 and 622 (e.g., calibration/serialdata streams provided as signal es by calibration signal generator1810).

FIG. 19 illustrates a Grey to binary converter (e.g., Gray to binaryblock 1850) for timing circuit 1710 in accordance with an embodiment ofthe disclosure. Gray to binary block 1850 operates similarly to Gray tobinary block 650 as described with reference to FIGS. 6, 10, and 11, butmay be implemented with a different arrangement of logic elements 1902,as shown in FIG. 19, where input g3 is coupled through a delay buffer1912 to output b3 to help reduce race conditions and/or other timingissues associated with operation of Gray to binary block 1850. FIG. 19shows an embodiment of Grey to binary block 1850 that can be implementedaccording to a limited number of logic elements 1902, which may includedelay buffer 1912 and three cross linked XOR logic gates as shown. Forexample, logic 1902 may be implemented by four chained 4-LUTs (e.g.,corresponding to four linked PLCs), which may be implemented entirelywithin a PLB of a PLD, with benefits similar to those discussed withreference to Grey code oscillator implementations described in FIGS. 7-9and Grey to binary block implementation described in FIGS. 10-11.

FIG. 20 illustrates a block diagram of calibration signal generator 1810for timing circuit 1710 in accordance with an embodiment of thedisclosure. As shown in FIG. 20, calibration signal generator 1810includes counter 2010 configured to provide serial data stream 1709(e.g., output a) and/or generate a training signal/calibration countbased on serial data stream 1709 (e.g., outputs b-g) to logic blocks2020, 2030, and 2050, logic blocks 2060 configured to generate variouscalibration enable signals (e.g., including registers configured tostore and provide calibration enable signals CAL2, CAL3, CAL4, and CAL5,corresponding to calibration serial data streams with high and lowcalibration time periods of 2, 3, 4, and 5 data cell widths), and serialdata signal generator 2040 configured to generate correspondingcalibration serial data streams and/or pass through serial data stream1709, as appropriate.

In typical operation, logic blocks 2020 and 2030 may be configured touse the calibration count provided by counter 2010 to generatecalibration timing signals t2-t5, which when provided to flip flop 2044through OR gate 2042 cause flip flop 2044 of serial data signalgenerator 2040 to generate various calibration serial data streams withdifferent associated time periods at output es of multiplexer 2048(e.g., which is then forwarded to Grey code oscillators 621 and 622 oftiming circuit 1710 in FIG. 18). Multiplexer 2048 is controlled byoutput g of counter 2010 (e.g., a most significant bit of counter 2010,which may correspond to a count of 32 in a binary counter), as sampledand stored by register 2046 according to serial data stream 1709, whichis output as a generic CAL enable signal by serial data signal generator2040 as shown. Once output g of counter 2010 is driven high, multiplexer2040 of serial data signal generator 2040 may be configured to passthrough serial data stream 1709 at output es, and counter 2010 may bedisabled/halted, thereby forcing multiplexer 2040 to pass through serialdata stream 1709 at output es until counter 2010 is reset by internalreset signal RST, as shown.

In addition, logic blocks 2050 and 2060 may be configured to use thecalibration count provided by counter 2010 and calibration timingsignals o0-o4 provided by logic blocks 2020 to generate calibrationenable signals CAL2, CAL3, CAL4, and CAL5, corresponding to the instantcalibration serial data stream generated by serial data signal generator2040 while the appropriate calibration enable signal CAL2, CAL3, CAL4,and CAL5 is driven high by logic blocks 2060.

FIG. 21 illustrates a block diagram of flip flop 2044 for serial datasignal generator 2040 of calibration signal generator 1810 in accordancewith an embodiment of the disclosure. As shown in FIG. 21, flip flop2044 may be implemented with three interconnected logic blocks 2110,2112, and 2114, as shown, and in some embodiments may be configured togenerate an output serial data stream with low and high time periodsapproximately equal in length to the high time period of a signalprovided to input D, as sampled according to the nearest transition of asignal provided to the latch input “>” of flip flop 2044. Moregenerally, flip flop 2044 may be implemented as a dual edge flip flopconfigured to latch an input at D at rising and falling transitions ofthe latch input “>” of flip flop 2044. In some embodiments, each logicblock 2110, 2112, and 2114 of flip flop 2044 may be implemented by asingle LUT/PLC within a PLD.

FIG. 22 illustrates a block diagram of calibration circuit 1720 forclock and/or data recovery deserializer 1700 in accordance with anembodiment of the disclosure. As shown in FIG. 22, calibration circuit1720 may include a number of different storage registers (e.g., lowstorage registers 2210-2216 and high storage registers 2220-2226)configured to store low/high calibration time periods measured by Greycode oscillators 621 and 622 of timing circuit 1710 (e.g., in the formof corresponding binary counts stored and provided by low/high storageregisters 1860 and 1862) as sampled according to internal clock signalCLK (e.g., generated by sample timing circuity of timing circuit 1710)and various calibration enable signals (e.g., CAL2, CAL3, CAL4, andCAL5). As also shown in FIG. 22, calibration circuit 1720 may alsoinclude a number of low and high integrators 2230-2234 and 2240-2244configured to combine low/high calibration time periods according tovarious low/high data patterns expected in a payload portion of serialdata stream 1709.

In some embodiments, low storage registers 2210-2216, high storageregisters 2220-2226, and/or low and high integrators 2230-2234 and2240-2244 may include additional logic configured to further manipulatelow/high calibration time periods to help generate various data patterntime periods configured to help detect particular data patterns within apayload portion of serial data stream 1709 (e.g., utilizing comparators1730-1738 and 1740-1746 in FIG. 17), such as bit shift logic, dividers,multipliers, and/or other logic and/or arithmetic operations. In thespecific embodiment illustrated in FIG. 22, low and high integrators2230-2234 and 2240-2244 are configured to sum two different calibrationtime periods and divide the result by 2, so as to provide a data patterntime period configured to differentiate expected payload time periodsaccording to a selection of expected data patterns (e.g., at comparators1730-1738 and 1740-1746 in FIG. 17). For example, logic block 2230 maybe configured to sum calibration time periods corresponding to 3 and 4data cells, for a total time period corresponding to 7 data cells, thendivide the sum by 2 to result in a data pattern time period (e.g., timeperiod differentiator value) corresponding to approximately 3.5 datacells, which can be used (e.g., at comparators 1730-1738 and 1740-1746)to reliably differentiate payload time periods corresponding toapproximately 3 data cells from payload time periods corresponding toapproximately 4 data cells. In general, calibration circuit 1720 mayinclude a different number and arrangement of storage registers and/orlogic blocks 2230-2234 and 2240-2244 according to a different expectedencoding of serial data stream 1709, for example, or according to adifferent comparison scheme to generate a recovered data signal from apayload portion of serial data stream 1709.

FIG. 23 illustrates a block diagram of decoder/decoder circuit 1770 forclock and/or data recovery deserializer 1700 in accordance with anembodiment of the disclosure. As shown in FIG. 23, decoder 1770 includesrecovered data splitter 2310 configured to receive the encoded recovereddata signal stored in registers 1750 and 1752 and generate six bit andfour bit split encoded data signals. The four bit split encoded datasignal may be provided to logic blocks 2320, 2322, and 2324 (e.g.,implemented respectively according to logic 2321, 2323, and 2325), whichmay be configured to decode the four bit split encoded data signal intothe three most significant bits (e.g., bits 5, 6, and 7) of a decodedrecovered data signal (e.g., decoded recovered data signal 1772). Thesix bit split encoded data signal may be provided to block 2340, whichmay be configured to decode the six bit split encoded data signal intothe five least significant bits (e.g., bits 0, 1, 2, 3, and 4) of thedecoded recovered data signal generated by decoder 1770. In someembodiments, block 2340 may be implemented using an embedded block RAMof a PLD, for example. Altogether, the elements of decoder 1770 may beconfigured to decode 8b10b encoded recovered data signal (e.g., reversean 8b10b encoding, as known in the art) into an eight bit recovered datasignal and/or format it as a parallel data signal, as shown.

FIG. 24 illustrates a block diagram of recovered data splitter 2310 fordecoder 1770 in accordance with an embodiment of the disclosure. Asshown in FIG. 24, recovered data splitter 2310 may include logic blocks2410-2412 and registers 2414-1418 configured to process and store a lowportion of an encoded recovered data signal (e.g., provided by register1750 in FIG. 17), logic blocks 2420-2422 and registers 2424-1428configured to process and store a high portion of an encoded recovereddata signal (e.g., provided by register 1752 in FIG. 17), logic blocks2430-2434 configured to generate word alignment signal WA based onsignals provided by other elements of deserializer 1700 (e.g., elementsof timing circuit 1710, which may generate RST, CLK, and/or CAL9/CAL),logic blocks 2440-2442 and registers 2444-2446 configured to word-alignthe processed/rearranged low and high portions of the encoded recovereddata signal, word-aligned data splitter 2450 configured to split theword aligned low and high portions of the encoded recovered data signalinto six bit and four bit split encoded data signals, registers 2460 and2462 configured to store and forward the six bit split encoded datasignal, and register 2464 configured to store and forward the four bitsplit encoded data signal.

In some embodiments, logic blocks 2430-2434 may be configured tosuppress word alignment signal WA during a calibration phase ofdeserializer 1700 (e.g., as indicated by calibration enable signalCAL9), to detect a beginning of a payload portion of serial data signal1709, as provided in the recovered data signal provided by registers1750 and/or 1752), after deserializer 1700 exits the calibration phase(e.g., by driving calibration enable signal CAL9 low), and to triggerword alignment signal WA (e.g., for a first time for a payload portionof serial data signal 1709) upon detecting the beginning of the payloadportion so as to set the first word alignment boundary, for example. Asshown in FIG. 24, the beginning of a payload portion of serial datasignal 1709 may be indicated by a high measured time period, provided tocomparators 1740-1746, that is long enough to change a state ofrecovered data signal bit ONE<5> after the calibration phase is complete(e.g., CAL9 is driven low), and after the training portion of serialdata stream 1709 (e.g., during which any measured transition timeperiods all correspond to a single data cell) is complete.

In various embodiments, logic blocks 2410-2412 and registers 2414-1418may be configured to convert the low portion of the encoded recovereddata signal (e.g., provided by register 1750 in FIG. 17) from a datapattern encoding corresponding to the selection of data patternsdetected by comparators 1730-1738 into a relatively compressed encoding(e.g., with a shorter bit width, yet retaining all information embeddedwithin the low portion of the encoded recovered data signal (e.g.,ZERO<2:5>). Such relatively compressed or different encoding may beconfigured to facilitate word alignment of the encoded recovered datasignal (e.g., performed by logic blocks 2440-2442 and registers2444-2446). Similarly, logic blocks 2420-2422 and registers 2424-1428may be configured to perform a similar conversion to the high portion ofthe encoded recovered data signal to facilitate word alignment of thehigh portion of the encoded recovered data signal (e.g., ONE<2:5>).

FIG. 25 illustrates a block diagram of word-aligned data splitter 2450for recovered data splitter 2310 in accordance with an embodiment of thedisclosure. As shown in FIG. 25, word-aligned data splitter 2450 mayinclude a number of input selector blocks 2510, each corresponding to aparticular bit mask 2511, feeding first layer of logic blocks 2520(e.g., each implemented according to a corresponding logic equation 2521for output f), which feeds second and third layers of logic blocks 2522and 2524 (e.g., implemented according to the indicated logic equations)and cross feeds first layer of logic blocks 2520 as shown. Second layerof logic blocks 2522 feeds third layer of logic blocks 2524, whichgenerates word aligned data signals (DAT<0> through DAT<9>) to be splitand output as six bit and four bit split encoded data signals as shownin FIG. 24. Logic block 2522 of first layer of logic blocks 2520associated with bit mask 0011 may be used to generate internal CLOCKsignal 2530, and logic block 2524 of first layer of logic blocks 2520associated with bit mask 1001 may be used to generate internal CLK6signal 2532. In various embodiments, internal CLK6 signal 2532 may beused to store the six bit split encoded data signal in register 2460,and internal CLOCK signal 2530 may be used to store and/or forward thesix bit split encoded data signal to register 2462 and the four bitsplit encoded data signal to register 2464, as shown in FIG. 24.

FIG. 26 illustrates a block diagram of a modulo 10 integrator (e.g.,logic block 2440) for recovered data splitter 2310 in accordance with anembodiment of the disclosure. As shown in FIG. 26, modulo 10 integrator2440 may include a logic block 2610 configured to sum two inputs, abuffer 2620 to pass a least significant bit of the sum output by logicblock 2610 as the least significant bit of the output of modulo 10integrator 2440, and three logic blocks 2622-2626 (e.g., implementedaccording to the indicated logic equations) configured to generate theremaining most significant bits of the output of modulo 10 integrator2440 each based on the remaining most significant bits of the sum andthe indicated logic.

FIG. 27 illustrates a method for operating a clock and/or data recoverydeserializer (e.g., deserializers 600, 1200, and/or 1700) in accordancewith an embodiment of the disclosure.

In operation 2702, a deserializer receives a serial data stream. Forexample, deserializers 600, 1200, and/or 1700 may be configured toreceive serial data streams 610 and/or 1709. In some embodiments,elements of deserializers 600, 1200, and/or 1700 may be configured toreceive calibration serial data streams, for example, that may begenerated by corresponding calibration signal generators 612 and/or 1810based on serial data streams 610 and/or 1709, as described herein.

In operation 2704, a deserializer measures time periods between signaltransitions of a serial data stream using a Grey code oscillator. Forexample, deserializers 600, 1200, and/or 1700 may be configured tomeasure high and low calibration and/or payload time periods betweensignal transitions of serial data streams 610 and/or 1709 and/orcorresponding calibration serial data streams, as described herein. Insome embodiments, the deserializer may be implemented with two Grey codeoscillators configured to measure low and high time periods betweensignal transitions separately by incrementing separate Grey code countsbetween the signal transitions and converting the Grey code countsapproximately at the signal transitions to binary counts eachcorresponding to a measured low or high time period, as describedherein.

In operation 2706, a deserializer generates a recovered data signalcorresponding to a serial data stream. For example, deserializers 600,1200, and/or 1700 may be configured to generate recovered data signals680, 1280, and/or 1772, as described herein, by comparing payload timeperiods/binary counts to one or more calibration time periods/binarycounts and/or expected data patterns to identify specific correspondingdata patterns and/or generate a corresponding recovered data signal. Insome embodiments, the recovered data signal may be an encoded recovereddata signal, for example, and the deserializer may be implemented with adecoder (e.g., decoder 1770) configured to decode the encoded recovereddata signal into a differently encoded and/or formatted recovered datasignal. For example, deserializer 1770 may be configured to generate a10 bit encoded recovered data signal at storage registers 1750 and 1752,and to generate a corresponding eight bit encoded and/or parallelformatted recovered data signal 1772 using decoder 1770.

FIG. 28 illustrates a second method for operating a clock and/or datarecovery deserializer (e.g., deserializers 600, 1200, and/or 1700) inaccordance with an embodiment of the disclosure.

In operation 2802, a deserializer increments a Grey code count betweensignal transitions in a serial data stream. For example, deserializers600, 1200, and/or 1700 may be configured to use Grey code oscillators621, 622, and/or 1222 to increment a Grey code count between signaltransition in serial data streams 610 and/or 1709 and/or correspondingcalibration serial data streams. In some embodiments, the deserializermay include two Grey code oscillators configured to increment two Greycode counts substantially asynchronously between adjacent negative andpositive signal transitions and/or adjacent positive and negative signaltransitions.

In operation 2804, a deserializer converts a Grey code count at signaltransitions in a serial data stream to a calibration binary count andpayload binary counts corresponding to time periods between the signaltransitions. For example, deserializers 600, 1200, and/or 1700 mayinclude one or more Grey code converters configured to convert Grey codecounts at signal transitions in serial data streams 610 and/or 1709and/or associated calibration serial data streams to a plurality ofbinary counts each corresponding to a time period between one or moresignal transitions in serial data streams 610 and/or 1709 and/orassociated calibration serial data streams. Such plurality of binarycounts may include calibration binary counts and/or payload binarycounts, for example.

In operation 2806, a deserializer stores a calibration binary count forcomparison to payload binary counts. For example, deserializers 600,1200, and/or 1700 may be configured to store a calibration binary countprovided by a Grey code converter in one or more of storage registers644, 1362, and 2210-2216 and 2220-2226, as described herein. In someembodiments, such calibration binary counts may be stored in variousintermediary storage registers, such as storage registers 1860 and/or1862. Upon storing the calibration binary counts, the various storageregisters may be configured to provide or forward the calibration binarycounts and/or associated data pattern time periods/binary counts to oneor more comparators (e.g., comparators 665, comparators of recoverycircuit portions 1264 and 1266, and/or comparators 1730-1738 and1740-1746) for comparison to payload binary counts and/or generation ofa recovered clock signal and/or a recovered data signal, as describedherein.

Thus, embodiments of the present disclosure provide a solution fordeserialization of serial data streams that can be implementedrelatively compactly in and with a greater degree of flexibility inplacement and routing for PLDs. Moreover, embodiments of the presentdeserializers can operate relatively efficiently from a cost perperformance perspective.

Where applicable, various embodiments provided by the present disclosurecan be implemented using hardware, software, or combinations of hardwareand software. Also where applicable, the various hardware componentsand/or software components set forth herein can be combined intocomposite components comprising software, hardware, and/or both withoutdeparting from the spirit of the present disclosure. Where applicable,the various hardware components and/or software components set forthherein can be separated into sub-components comprising software,hardware, or both without departing from the spirit of the presentdisclosure. In addition, where applicable, it is contemplated thatsoftware components can be implemented as hardware components, andvice-versa.

Software in accordance with the present disclosure, such as program codeand/or data, can be stored on one or more non-transitory machinereadable mediums. It is also contemplated that software identifiedherein can be implemented using one or more general purpose or specificpurpose computers and/or computer systems, networked and/or otherwise.Where applicable, the ordering of various steps described herein can bechanged, combined into composite steps, and/or separated into sub-stepsto provide features described herein.

Embodiments described above illustrate but do not limit the invention.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the present invention.Accordingly, the scope of the invention is defined only by the followingclaims.

We claim:
 1. A method comprising: receiving a serial data stream;measuring payload time periods between signal transitions in a payloadportion of the serial data stream using at least one Grey codeoscillator; and generating a recovered data signal corresponding to thepayload portion of the serial data stream by, at least in part,comparing the measured payload time periods to one or more calibrationtime periods.
 2. The method of claim 1, wherein the measuring thepayload time periods comprises: incrementing, by the Grey codeoscillator, a Grey code count between the signal transitions in thepayload portion of the serial data stream; and converting the Grey codecount approximately at the signal transitions to a plurality of binarycounts each corresponding to one of the payload time periods.
 3. Themethod of claim 1, wherein the Grey code oscillator comprises a firstGrey code oscillator, and wherein the measuring the payload time periodscomprises: incrementing, by the first Grey code oscillator, a first Greycode count from zero between negative and adjacent positive signaltransitions in the payload portion of the serial data stream; convertingthe first Grey code count approximately at the adjacent positive signaltransitions to a plurality of low binary counts corresponding to lowpayload time periods between the negative and adjacent positive signaltransitions; incrementing, by a second Grey code oscillator, a secondGrey code count from zero between positive and adjacent negative signaltransitions in the payload portion of the serial data stream; andconverting the second Grey code count approximately at the adjacentnegative signal transitions to a plurality of high binary countscorresponding to high payload time periods between the positive andadjacent negative signal transitions.
 4. The method of claim 3, whereinthe generating the recovered data signal comprises, for each pair ofadjacent low and high time periods of the payload portion of the serialdata stream: comparing the corresponding low binary count to one or morelow calibration binary counts and/or data patterns to identify acorresponding low data pattern associated with the pair of the adjacentlow and high time periods; comparing the corresponding high binary countto one or more high calibration binary counts and/or data patterns toidentify a corresponding high data pattern associated with the pair ofthe adjacent low and high time periods; and combining the low and highdata patterns to form a portion of the recovered data signalcorresponding to the pair of adjacent low and high time periods.
 5. Themethod of claim 1, wherein the generating the recovered data signalcomprises: generating a recovered clock signal corresponding to theserial data stream by, at least in part, comparing the measured payloadtime periods to a base calibration time period and initiating arecovered clock signal transition when the measured payload time periodexceeds the base calibration time period; and generating the recovereddata signal by sampling the payload portion of the serial data stream atthe recovered clock signal transitions.
 6. The method of claim 1,wherein the payload portion of the serial data stream comprises anencoded data stream and the recovered data signal comprises acorresponding encoded data signal, the method further comprising:decoding the recovered data signal into an eight bit encoded datasignal.
 7. The method of claim 1, further comprising: detecting atraining portion in a preamble of the serial data stream; generating oneor more calibration serial data streams based, at least in part, on thetraining portion of the serial data stream; measuring the one or morecalibration time periods between calibration signal transitions in thecorresponding one or more calibration serial data streams using the atleast one Grey code oscillator; and storing the one or more calibrationtime periods in corresponding one or more storage registers.
 8. Themethod of claim 7, wherein the measuring the one or more calibrationtime periods comprises: incrementing, by the Grey code oscillator, aGrey code count between the calibration signal transitions in thecorresponding one or more calibration serial data streams; andconverting the Grey code count approximately at the calibration signaltransitions to a plurality of calibration binary counts eachcorresponding to one of the one or more calibration time periods.
 9. Themethod of claim 7, wherein the Grey code oscillator comprises a firstGrey code oscillator, and wherein the measuring the one or morecalibration time periods comprises: incrementing, by the first Grey codeoscillator, a first Grey code count from zero between negative andadjacent positive signal transitions in the corresponding one or morecalibration serial data streams; converting the first Grey code countapproximately at the adjacent positive signal transitions to a pluralityof low calibration binary counts corresponding to the one or morecalibration time periods between the negative and adjacent positivesignal transitions; incrementing, by the second Grey code oscillator, asecond Grey code count from zero between positive and adjacent negativesignal transitions in the corresponding one or more calibration serialdata streams; and converting the second Grey code count approximately atthe adjacent negative signal transitions to a plurality of highcalibration binary counts corresponding to the one or more calibrationtime periods between the positive and adjacent negative signaltransitions.
 10. A computer-implemented method comprising: detecting, ina design for a programmable logic device (PLD), a serial data streaminput and a deserializer block configured to generate a recovered datasignal corresponding to a payload portion of a serial data streamprovided by the serial data stream input; and synthesizing the designinto a plurality of PLD components, wherein the plurality of PLDcomponents are configured to implement: a Grey code oscillator for thedeserializer block in the design, wherein the Grey code oscillator isconfigured to measure payload time periods between signal transitions inthe payload portion of the serial data stream provided by the serialdata stream input; and at least one comparator for the deserializerblock in the design, wherein the at least one comparator is configuredto compare the measured payload time periods provided by the Grey codeoscillator to one or more calibration time periods to generate therecovered data signal.
 11. The computer-implemented method of claim 10,wherein the plurality of PLD components are further configured toimplement: a Grey code converter for the deserializer block in thedesign, wherein the Grey code converter is configured to convert a Greycode count provided by the Grey code oscillator approximately at thesignal transitions to a plurality of binary counts each corresponding toone of the payload time periods.
 12. The computer-implemented method ofclaim 10, wherein the plurality of PLD components are further configuredto implement: at least one storage register for the deserializer blockin the design, wherein the at least one storage register is configuredto store one or more calibration binary counts corresponding to the oneor more calibration time periods and provide the one or more calibrationbinary counts to the at least one comparator.
 13. Thecomputer-implemented method of claim 10, wherein the payload portion ofthe serial data stream comprises an encoded data stream and therecovered data signal comprises a corresponding encoded data signal,wherein the plurality of PLD components are further configured toimplement: a decoder for the deserializer block in the design, whereinthe decoder is configured to decode the recovered data signal into aneight bit encoded data signal.
 14. The computer-implemented method ofclaim 10, wherein the plurality of PLD components are further configuredto implement: a data recovery circuit for the deserializer block in thedesign, comprising the at least one comparator, wherein the datarecovery circuit is configured to receive the one or more calibrationtime periods and the measured payload time periods and generate arecovered data signal corresponding to the serial data stream, andwherein the recovered data signal is based, at least in part, on thechange in the output state of the at least one comparator.
 15. Thecomputer-implemented method of claim 10, wherein the plurality of PLDcomponents are further configured to implement: a calibration signalgenerator for the deserializer block in the design, wherein thecalibration signal generator is configured to detect a training portionin a preamble of the serial data stream and/or generate one or morecalibration serial data streams based, at least in part, on the trainingportion of the serial data stream.
 16. The computer-implemented methodof claim 10, wherein the Grey code oscillator comprises a first Greycode oscillator, and wherein the plurality of PLD components are furtherconfigured to implement: a second Grey code oscillator for thedeserializer block in the design, wherein the first Grey code oscillatoris configured to increment a first Grey code count from zero betweennegative and adjacent positive signal transitions in the payload portionof the serial data stream, and the second Grey code oscillator isconfigured to increment a second Grey code count from zero betweenpositive and adjacent negative signal transitions in the payload portionof the serial data stream.
 17. The computer-implemented method of claim16, wherein: the first and/or second Grey code oscillators are eachimplemented entirely within a programmable logic block of the PLD. 18.The computer-implemented method of claim 10, further comprising:receiving the design; routing connections between the plurality of PLDcomponents; generating configuration data to configure physicalcomponents of the PLD in accordance with the plurality of PLD componentsand a routing for the design; and programming the PLD with theconfiguration data.
 19. A PLD comprising configuration data comprisingthe plurality of PLD components synthesized according to thecomputer-implemented method of claim
 10. 20. A system to perform thecomputer-implemented method of claim 10, the system comprising: aprocessor; and a memory adapted to store a plurality of computerreadable instructions which when executed by the processor are adaptedto cause the system to perform the computer-implemented method of claim10.